1. Field of the Invention
The present invention relates to an integrated circuit, and more particularly to an apparatus and a method adapted to use one-time programming (OTP) devices for multiple-time programming (MTP).
2. Description of the Related Art
In a proceeding of an integrated circuit manufacture, the electrical parameters of each integrated circuit may vary from lot to lot, and vary from wafer to wafer of the same lot, and even vary from die to die of the same wafer. There are different process variations such as deviation of ion implantation, deviation of gate oxide thickness, and error in etching. Such variation of process will cause frequency deviation of an oscillator, or voltage deviation of a regulator. If the electrical parameters of an integrated circuit vary beyond the specification, e.g. over 5% deviation of the IC specification, the product is deemed failed during testing process. Accordingly, the IC manufacturer should perform some post-fabrication fine-tuning of the parameters of integrated circuits mentioned above to improve production yield. Since the electrical characteristics mentioned above change along with fabricating parameters, one-time programming (OTP) devices, e.g. poly fuse and metal wire, are used for post-fabrication fine-tuning for electrical characteristics consistency within a lot, thus improve the production yield. The OTP method can effectively improve production yield of integrated circuits.
The OTP method applied to integrated circuits includes: laser trimming or poly fusing (E-fuse). The laser-trimming method is to blow a metal wire with high-energy laser. The poly-fusing method is to blow the poly fuse with a large current or to change the resistance of the poly fuse caused by electron migration phenomenon under large current. Then a reading circuit detects whether the metal wire or the poly wire is open or whether the resistance of the poly fuse is changed. By the detection, it can be determined whether the OTP device is programmed or not. The programming step is an irreversible, destructive operation. It means that the OTP device can be programmed only once and cannot be repaired.
After the OTP device is programmed, the poly fuse of the OTP device is blowed and cannot be repaired. The OTP device, therefore, cannot be multiple-time programmed. It is desired that the electrical characters of integrated circuits can be repetitively changed. For the example of STN LCD drivers, the operating voltage VLCD of the STN LCD drivers has been adjusted to a precise value during the testing process. During STN LCD module assembling process, the operating voltage VLCD of the STN LCD drivers may shift due to the characteristic shift of liquid crystal or the gap deviation of electrode on glass. The shift of operating voltage will ruin the contrast ratio of STN LCD. Accordingly, it is desired to fine tune the operating voltage VLCD of the STN LCD drivers for the purpose of improving production yield of the STN LCD modules.
In order to perform multiple-time programming, the prior art technique adopts multiple-time programming (MTP) devices. The MTP devices can be, for example, EPROM, EEPROM or FLASH. Although the MTP devices can serve multiple-time programming functions, the manufacturing costs of the MTP devices are more expensive. For the 0.35 μm 3.3V/18V high voltage process of STN LCD driver, to integrate the MTP device like EEPROM requires several additional masks. The additional masks increase the manufacturing costs. In addition to the higher costs, the manufacturing time and lead-time must be extended. By the increase of additional mask process, the yield of integrated circuits may decline. Few foundry companies are capable of fabricating such MTP devices and few MTP processes can be selected. Therefore, it is hard to find out an appropriate foundry company to fabricate MTP devices and the situation may risk productivity dispersion.